The upload of "Calendar" failed. There was a problem with the request.

We've been using Outlook 2010 at the office for years, and for years users have been able to publish their calendars to an in-house server. Some days ago that stopped working for one user. I've checked the Publish Calendar Settings > Advanced, toggled the 'Update this calendar with the server's recommended frequency' checkbox (left it check), then Clicked OK, OK and got the message, "The upload of 'Calendar' failed. The next upload attempt occurs with the next send/receive. There was a problem with the request." Of course, no mention here of what the problem was.

Following some web advice, I tried Remove from Server, but got the message, "The Calendar was not removed form the server. To remove this calendar, you must delete the file on the server." So, I did that, but still nothing. I still get the "The Calendar was not removed ..." message when I try the Remove from Server option, even though the calendar no longer exists on the server, and I got the follow-up message, "The calendar could not be removed automatically from the server. Updates to this calendar will continue to be published until you remove the calendar from the server. Try to remove it again later." Well, the calendar is removed and updates are not happening. So, I put the calendar .ics file back on the server.

I'm stuck. I'd like to get this calendar re-publishing. What's my solution?

I figured out the reason this started happening in the first place. While messing with something else I turned off the WebDAV service. This affected all Outlook users. However, when I turned the service back on other Outlook users' calendars resumed updating, but this particular user's calendar did not. I kept getting the same "The upload of 'Calendar' failed" error.

I tried everything I could think of including un-joining and re-joining the domain. Repairing Office, un-installing and re-installing Office. Image restoring the entire workstation to earlier dates. Restoring the PST file to earlier dates. Nothing worked. Finally, I had to remove the user's Outlook profile (after exporting Calendar and Contacts) and re-create it. I imported the saved Contacts and Calendars and re-published the calendar and it all started working again. Unfortunately, this user (who is the organization Director) lost all his color category settings which he lives and dies by. As far as I can tell, there is no way to export and import these settings.

Categories from the events or just the colors? Are the category names in the exported files? IMAP doesn't support categories, but I would expect them to export if they are assigned. (I'll need to test it to confirm.)

No, I know IMAP doesn't support Outlook categories (it does support tags used by e.g. Dovecot/Thunderbird). My understanding is that Outlook category/colors for emails are kept in the PST file. I'm only looking for color categories on the email, not the calendar/events. In the past, when installing Outlook from scratch and re-creating the user's account (e.g. new machine), I've had the user open his old PST file and browse those message for color categories settings and manually set his current mailbox message one-by-one. As you can imagine, this is labor intensive and this user is disinterested in doing that again. You once upon a time gave me a VB script to extract the color category settings from Outlook. I've used that to set tags for Thunderbird/IMAP users who migrated from Outlook (doable since we host our own IMAP/Dovecot server). It would be nice if there were a way to import this information to the new Outlook account messages.

Correct, the master category list is stored in the default data file. When you removed the profile, it removed the data file - so you lost the master list. The mail lost the categories because they dont sync back to imap servers - so when the new data file synced, there were not categories.